1. Field of the Invention
The present invention relates to a preform structure, a composite aluminium or aluminium alloy component composited with the preform structure, and methods for producing the preform structure and the composite aluminium or aluminium alloy component composited with the preform structure.
2. Description of the Related Art
Components such as ring grooves of pistons disposed in an automobile engine, brake disk rotors in a braking system, and valve lifters of the engine have sliding portions which slide on other members, and such sliding portions need a desired wear and abrasion resistance. It is conventionally known that when such components are made of an aluminium or aluminium alloy, the aluminium or aluminium alloy is used as a base metal and is reinforced with a reinforcing material having a good wear and abrasion resistance by the molten metal mixing method.
However, in the above-mentioned conventional method, all of the components are reinforced with the reinforcing material as well as the sliding portions which need the wear and abrasion resistance. Therefore, a very large amount of the reinforcing material has to be used and thus manufacturing cost is increased. Further, the reinforcing or compositing process becomes complex, since the molten metal with a desired viscosity has to be provided so that the reinforcing material is not concentrated in the molten metal by floating thereof.
It is disclosed in, for example, Japanese Patent Laid-Open No. 3-151158 that a preform structure is made by sintering a mixture of SiC whiskers and aluminium alloy powders to be a predetermined shape, after which the preform structure is set on a predetermined place in a casting mould, molten aluminium is then poured at a high pressure into the casting mould, and the preform structure is composited with the molten aluminium.
According to this method, the component partially having a reinforced portion can be made. However, since too many SiC whiskers tend to be contained in the reinforced portion, the pouring pressure of the molten aluminium has to be high during the reinforcing process, and it is difficult to produce a necessary composite material having a low volume ratio. Therefore, the manufacturing cost becomes high and the obtained composite material might break other components which slide thereon.
Japanese Patent Publication No. 63-54057 discloses a method for efficiently and inexpensively producing an alloy with a good efficiency, a low cost and a predetermined structure. A porous body or preform structure are made of fine solid members which are a compound of a first metal and oxygen. The porous body is dipped into a molten metal including a second metal, and then the molten metal is pressurized so as to infiltrate into the porous body. The oxide of the first metal is deoxidized while the second metal is oxidized. Thus, an alloy is produced by one portion of the molten metal and the porous body, while the remaining portion of the molten metal becomes the metal oxide which is finely dispersed into the alloy.
Japanese Patent Laid-Open No. 63-295050 discloses a method for producing a composite metal component. According to the method, a small amount of reinforcing material is homogeneously dispersed into the metal components. That is, a scaffolding structure having a predetermined pattern is made of a fiber material including cellulose and the like and plastic fibers. Fibers and particles of reinforcing materials are dispersed along the scaffolding structure, and thereafter the pattern of the scaffolding structure is dissipated or decomposed in the molten metal so as to be reinforced or composited with the molten metal. Further, alumina fibers and the like are used as the pattern so as to assure the reinforcing material is dispersed.
Ceramic particles such as titanium dioxide and SiC are low in cost and have a wear and abrasion resistance as reinforcing materials, and therefore they are more preferable than whiskers, short fibers and the like. When a preform structure is made of reinforcing materials composed of such ceramic particles, which particles have been pressurized and sintered as disclosed in Japanese Patent Laid-Open No. 3-151158, the volume ratio of the ceramic particles becomes high, the volume ratio is difficult to control as in the case when reinforcing materials are made of the whiskers, and the volume ratio has a lower limit. Therefore, when the high pressure aluminium casting is done, the molten aluminium or alloy is not dispersed into the preform structure and therefore the preform structure might be broken by the high pressure.
The above-mentioned method disclosed in Japanese Patent Publication No. 63-54057 can be applied when an oxide such as titanium dioxide is used as the ceramic particles, but can not be applied when a non-oxide is used. However, even if titanium dioxide is used as the ceramic particles and this method is applied, the preform structure is still easily broken during oxidation and deoxidation reactions. Further, since a widely used aluminium alloy includes silicon, the titanium is produced by a deoxidation reaction of the titanium dioxide and the titanium is combined with the silicon and the aluminium to produce an Al--Ti--S compound. Though this compound increases hardness and wear and abrasion resistance of the preform structure, the preform structure becomes brittle and thus is more easily broken.
When the above-mentioned method disclosed in Japanese Patent Laid-Open No. 63-295050 is used, the amount of the reinforcing materials can be preferably decreased, but the reinforcing materials can not be homogeneously dispersed along the pattern and therefore the wear and abrasion resistance of the preform structure is decreased. Further, when the pattern is dissipated by the molten aluminium, an aluminium carbide is produced by which the preform structure becomes brittle. Still further, when alumina fibers and the like are used as the pattern, a large number of the alumina fibers have to be added, and therefore the strength of the preform structure is lowered and it is difficult to infiltrate into the preform structure because of a bad air permeability.